A lot depends on where you live. Cold weather is gentler to batteries than hot weather. Here in the oven, also known as Arizona, regular flooded cell batteries will last maybe 24 months. Better grades, at higher cost, will last a little longer. When a flooded cell battery dies, it just dies, usually with no warning. So the battery that got you to the grocery to buy the 5 gallons of ice cream for your kid's July birthday party will be dead when you bring the ice cream back to the car. An AGM battery will give you some warning a few months ahead.
That said, I used to use Optima batteries I bought at Costco until they moved their manufacturing to Mexico. Costco quit selling them because the Mexico-made Optima batteries came back so often. I got six years (yes, six years) out of a set of Batteries Plus house brand AGM batteries by keeping them on a float charger when I wasn't using the truck.
I replaced them with the house brand O'Reilly AGM batteries last year. So far, so good. I will use AGM batteries as long as I can, expensive though they may be, because of the "I am about to die" warning and because they don't cause corrosion of the terminals and under the battery trays. The corrosion causes all sorts of electrical gremlins . . .
On the other hand, a colleague in Wyoming got nine years out of the OEM batteries in her 2008 CTD and actually complained about it. Different climate.